It's All Connected: Global Circulation

The lab activity described here was adapted by Erin Bardar of TERC for the EarthLabs project.

Summary and Learning Objectives

Students are introduced to the global circulation patterns of the atmosphere and the oceans, and investigate how those circulation patterns might influence their local region. Students use computer models to test predictions of ocean currents.

After completing this investigation, students should be able to:

trace pathways of wind and water on a world map to and from their region, and across an ocean to other parts of the Earth;

describe specifically how their region is connected as a system to others across the Earth by identifying what their wind and water carry and where the wind and water go; and

write about what activities in their region might affect other regions, and what activities in other regions might affect theirs

Activity Overview and Teaching Materials

In Part A: Students are introduced to the global circulation patterns of the atmosphere and the oceans, and investigate how those circulation patterns might influence their local region.

In Part B: Students study surface ocean currents and then predict the pathway of a floating object dropped into the ocean at a particular point, maybe one closest to their own region. Then, using a computer model of ocean currents, they test their predictions.

Printable Materials

To download one of the PDF or Word files below, right-click (control-click on a Mac) the link and choose "Save File As" or "Save Link As."

For more information about circulation of the atmosphere and the oceans , read the section titled Background Information under Additional Resources below.

Teaching Notes and Tips

In Part A: Students move back and forth between learning about global circulation patterns of air and water, and looking for connections between the local area and those global circulations. Part of this work involves tracing the path of a local stream until it joins the global ocean circulation. Resources that allow you to investigate the local-to-global connections are not provided in this Lab. You'll need to gather those resources and explore the possibilities. What pathways do your local streams follow as they wind their way toward the ocean? (Or might a local stream actually terminate at an endorheic body of water, which has no outflow, such as the Great Salt Lake?)

In Part B: The Ship Drift model is an engaging tool that makes the topic of ocean currents become very concrete and alive; it's interesting and fun to use.

Here are some notes about using the model:

To see a map of ocean currents in a particular month, select the month in the drop-down menu and then click the PopUp Map button. The map of ocean currents on the home page is interactive but it does not change when you change the month. The PopUp maps are the maps that students use to make their predictions about the path along which ocean currents may carry an object during a particular time of year. You can open multiple PopUp maps on your computer screen to compare ocean currents across the seasons.

To see the probable paths that a set of five drifters (buoyant objects that remain near the ocean surface) might follow over the course of five years, select a month in the drop-down menu and click on the map of ocean currents on the home page. A new window will open showing the probable paths of the 5 drifters. You can open multiple drifter path maps on your computer screen to see how dropping a drifter in the same spot* can vary across the seasons.

* The latitude and longitude you select on the home page map may not be identical to the coordinates that appear at the bottom of the drifter path map that opens, but they will be very close. The home page map displays latitude and longitude in 5 degree increments.

For more information about the Ship Drift model, visit Navigating the Ocean on NASA's Ocean Motion Web page.

Assessment

You can assess student understanding of topics addressed in this Investigation by grading their responses to the Stop and Think questions.

State and National Science Teaching Standards

(1) Scientific processes. The student conducts laboratory and field investigations for at least 40% of instructional time using safe, environmentally appropriate, and ethical practices. The student is expected to:

(A) demonstrate safe practices during laboratory and field investigations.

(2) Scientific processes. The student uses scientific methods during laboratory and field investigations. The student is expected to:

(E) demonstrate the use of course equipment, techniques, and procedures, including computers and web-based computer applications;

(3) Scientific processes. The student uses critical thinking, scientific reasoning, and problem solving to make informed decisions within and outside the classroom. The student is expected to:

(A) in all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student;

(B) communicate and apply scientific information extracted from various sources such as current events, news reports, published journal articles, and marketing materials.

(11) Science Concepts. Solid Earth. The student knows that Earth's surface continuously changes over long and short time scales in ways involving dynamic and complex interactions among Earth's subsystems. The student is expected to:

(13) Science concepts. Fluid Earth. The student knows that the Fluid Earth is composed of the hydrosphere and atmosphere subsystems that interact on various time scales with the biosphere and geosphere. The student is expected to:

(D) discuss mechanisms, such as atmospheric carbon dioxide concentration, major volcanic eruptions, changes in solar luminance, giant meteorite impacts, and human activities that result in significant changes in Earth's climate.

(14) Science concepts. FluidEarth. The student knows that Earth's global ocean, powered by the Sun, is a major driving force for weather and climate through complex atmospheric interactions. The student is expected to:

12ASI1.3 Use technology and mathematics to improve investigations and communications. A variety of technologies, such as hand tools, measuring instruments, and calculators, should be an integral component of scientific investigations. The use of computers for the collection, analysis, and display of data is also a part of this standard. Mathematics plays an essential role in all aspects of an inquiry. For example, measurement is used for posing questions, formulas are used for developing explanations, and charts and graphs are used for communicating results.

12ASI1.6 Communicate and defend a scientific argument. Students in school science programs should develop the abilities associated with accurate and effective communication. These include writing and following procedures, expressing concepts, reviewing information, summarizing data, using language appropriately, developing diagrams and charts, explaining statistical analysis, speaking clearly and logically, constructing a reasoned argument, and responding appropriately to critical comments.

Physical Science (12BPS)

Interactions of energy and matter

12BPS6.1 Waves, including sound and seismic waves, waves on water, and light waves, have energy and can transfer energy when they interact with matter.

Earth and Space Science (12DESS)

Energy in the earth system

12DESS1.3 Heating of earth's surface and atmosphere by the sun drives convection within the atmosphere and oceans, producing winds and ocean currents.

12DESS1.4 Global climate is determined by energy transfer from the sun at and near the earth's surface. This energy transfer is influenced by dynamic processes such as cloud cover and the earth's rotation, and static conditions such as the position of mountain ranges and oceans.

Additional Resources

Background Information

Atmospheric Circulation

The global circulation of air drives some of the Earth's ocean currents and helps to redistribute the solar energy that reaches Earth, moderating climate and impacting environments for all life on Earth. Without that circulation and redistribution of solar energy, the equatorial regions would be hotter and the polar regions colder.

What drives this atmospheric circulation? It's not simply solar energy; it's solar energy interacting with the rotating sphere that is our planet. The differential heating that occurs when the sun heats a sphere (the earth) plays a significant role. Another factor is the Coriolis effect, which results from the fact that the rotational speed of our spherical planet varies with latitude.

Differential Heating

Earth's solar energy is most concentrated in the region of the equator. This heating causes warm air to rise, which creates a general area of low pressure at the equator. As the rising air cools and starts to fall back toward Earth it spreads into both the northern and southern hemispheres (see figure) and returns to the surface of Earth at approximately 30 degrees north and south of the equator. That cooled air is then drawn back towards the low-pressure area at the equator and repeats the circulation. This circulation creates what are known as the Hadley Cells. (See figure.)

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This image gives a three dimensional view of the global wind circulation patterns dues to unequal heating at the equator and the poles.

Provenance: Image from NASA's Remote Sensing Tutorial: The Water Planet - Meteorological, Oceanographic and Hydrologic Applications of Remote Sensing. https://www.fas.org/irp/imint/docs/rst/Sect14/Sect14_1c.htmlReuse: This item is in the public domain and maybe reused freely without restriction.

Something similar but opposite happens in the polar regions. The solar energy falling on Earth's surface in the polar regions is spread over a much greater surface area. The resulting colder air creates high-pressure areas at Earth's surface, with cold air flowing away from the poles. As that air reaches lower latitudes it is subject to more intense solar energy, warms, rises, and is drawn toward the low-pressure areas that are high above the poles. This circulation creates two additional cells in the polar regions.

In between the Hadley and polar cells in each hemisphere is a third cell of air circulation.

Coriolis Effect

What is the Coriolis Effect, and why does it occur? First think just about the solid Earth. As the Earth rotates, a point on the equator moves in a large circle, and travels more than 38,000 km during one full revolution, or in 24 hours. Its rotational speed is approximately 1600 km/hr. During that same 24 hours, a point close to one of the poles makes a much smaller circle in the course of one day, and travels just a tiny fraction of the distance, so it's rotational speed is significantly slower than a point on the equator. In fact, a point on Earth's equator rotates at a greater speed than any point north or south of the equator.

If Earth did not rotate, air flowing from a higher latitude toward the equator would move directly south or north (depending on the hemisphere). However, because of the rotation, air that flows toward the equator is moving from a latitude where its rotational speed is less to a latitude where the rotational speed is more. As a result, that air rotates more slowly than the land below it, so it "falls behind" and it is deflected toward the west (see figure below). This produces a wind at the equator that flows from east to west.

Likewise, air flowing away from the equator and towards a higher, more slowly rotating latitude will rotate more rapidly than the land below, and will deflect towards the east to produce a west-to-east wind.

Study the figure above to draw the connections between the cells that result from differential heating of the Earth and the major patterns of global atmospheric circulation that result from cell circulation and the Coriolis effect.

While the bands of circulating air cells and the Coriolis effect drive the general atmospheric circulation patterns, that circulation is also influenced by local conditions and is much more complex than the simplified illustrations suggest.

This image below shows twenty years of cyclone paths in the Atlantic. Can you see evidence of the general atmospheric circulation patterns?

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Cyclone paths in the Atlantic. Click image to enlarge.

Ocean Circulation

Read the National Oceanic and Atmospheric Administration's concise, well-illustrated resources that explain the driving forces behind ocean circulation. Some of these are related to the winds described above; others have a very different driving mechanism (a combination of temperature and salinity). The sections that address Surface Ocean Currents and The Global Conveyer Belt are just two of the topics covered in the Currents section of this education Web site.